The present invention relates to improvements in a split type multicylinder internal combustion engine operable on less than all of its cylinders when the engine load is below a given value.
It is known that to increase the efficiency of a multicylinder internal combustion engine, the number of cylinders on which the engine operates under predetermined engine operating conditions can be reduced, particularly under conditions of low engine load. For this purpose, control means are provided which disable a number of cylinders in a multicylinder internal combustion engine by blocking the flow of air-fuel mixture to disabled cylinders under low load conditions. The disablement of some of the cylinders of the engine increases the load on those remaining in operation and, as a result, the energy conversion efficiency is increased. It is common practice in automotive vehicle engines to suppress maximum combustion temperature so as to minimize NOx production in the cylinders by introducing exhaust gases into the engine intake manifold under intake manifold vacuum. For such split type engines, however, it has been found extremely difficult to maintain an EGR ratio optimum to minimize the emission from the engine of noxious pollutants since the intake manifold vacuum varies according to the engine being in full or split engine operation.
The present invention provides an improved split type multicylinder internal combustion engine wherein accurate EGR ratio control is made over the entire engine operating range to aid in the reduction of exhaust emissions.